Quickest, easiest way to tell is to remove the front panel of the dishwasher and look at the wires going to the control. One of the connectors will have only 2 wires to it, a red and a gray,(note that these 2 wires will be larger gauge than any of the wires going to the other connectors). Unplug it from the control and test from one wire to the other. This tests the continuity of the heater,thermostat, and associated wiring. If you read a resistance there is no problem with the heater and the problem is in the control. If it reads open the heater needs to be replaced. Thats all there is to it! =]